CCIE chapter 7 – RIP v2
Resources:
Cisco Press CCNP Self-Study BCMSN Official Exam Certification Guide 3th Edition
CCIE Professional Development Routing TCP-IP Volume I
CCIE Routing and Switching Exam Certification Guide 3rd Edition
Rip V2 feature summery
Function
Transport
Metric Hop count,
Hello interval
Update destination
Update interval
Full or partial updates
Triggered updates Yes,
Description
UDP, port 520.
with 15 as the maximum usable metric, and 16 considered to be infinite.
None; RIP relies on the regular full routing updates instead.
Local subnet broadcast (255.255.255.255) for RIPv1; 224.0.0.9 multicast for RIPv2.
30 seconds.
Full updates each interval. For on-demand circuits, allows RIP to send full
updates once, and then remain silent until changes occur, per RFC 2091. Full
updates each interval.
when routes change.
Multiple routes to the
same subnet
Allows installing 1 to 6 (default 4) equal-metric routes to the same subnet in a single
routing table.
Authentication*
Allows both plain-text and MD5 authentication.
Subnet mask in
updates*
RIPv2 transmits the subnet mask with each route, thereby supporting VLSM
making RIPv2 classless. This feature also allows RIPv2 to support discontiguous
networks.
VLSM*
Route Tags*
Next Hop field*
Supported as a result of the inclusion of subnet masks in the routing updates.
Allows RIP to tag routes as they are redistributed into RIP.
Supports the assignment of a next-hop IP address for a route, allowing a router
to advertise a next-hop router that is different from itself.

RIPv2-only features
RIP send all connected routes and all RIP learnt router every “update interval”
Rip doesn’t have any neighbor relationships, all it does is send its update on multicast address 224.0.0.9 out all non passive interfaces
Rip sends out a request message on all non passive interfaces, if a response is heard it sends the full RIP routing table ( rip learn’t
routes + connected routes) out that interface.
By default rip will auto summarise to the classfull boundary
Rip only uses Hop count as its Metric with a maximum hop count of 15
Rip metric works by the advertising router incrementing the hope count not the receiving router, so if a router has a net with a metric
of 2 it will advertise it as a metric of 3.
Rip can send 25 route updates per update packet
16 bit field for route tag
RIP Convergence and Loop Prevention
Rip has no loop prevention built into the protocol structure rather it relies on general
tools that distance vector route protocols rely on. These tools generally increase the
convergence time of the routing protocol.
Split horizon, a route isn’t advertised out the physical interface that it is learn’t
Route poisoning/Poison reverse, when a route failure is detected the router advertise that
route with metric 16 to the router it learnt it from as well as all
networks that it learn’t form that router.
Triggered updates —As soon as a routing process changes a metric for a network in its routing
table, it sends an update with the metric set to a value that states it is unusable. In RIP, this value
is infinity, that is, 16. Triggered updates inform the other routers immediately. If there is a
problem in the network, all the affected routers go into holddown immediately instead of
waiting for the periodic timer
Holddown timer
A per-route timer (default 180 seconds) that begins when a route’s metric changes to a
larger value. The router does not add an alternative route for this subnet to its routing
table until the Holddown timer for that route expires.
Invalid timer A per-route timer that increases until it receives a routing update that confirms the
route is still valid, upon which the timer is reset to 0. If the updates cease, the Invalid
timer will grow until it reaches the timer setting (default 180 seconds), after which the
route is considered invalid.
Flush timer
A per-route timer that is reset and grows with the Invalid timer. When the Flush timer
mark is reached (default 240 seconds), the router removes the route from the routing
table and accepts new routes to the failed subnet.
The steps for RIPv1 and RIPv2 convergence are as follows:
1. When the local router sees a connected route disappear, it sends a flash update and removes the
route entry from its table. This is called a triggered update with poison reverse.
2. The receiving routers send flash updates and put the affected route in holddown.
3. The originating router queries its neighbor for alternative routes. If the neighbor has an
alternative route, it is sent; otherwise, the poisoned route is sent.
4. The originating router installs the best alternative route that it hears because it has purged the
original routes.
5. Routers that are in holddown ignore the alternative route.
When the other routers emerge from holddown, they will accept the alternative route.
Convergence takes the time for detection, plus holddown, plus the number of routing updates (equal
to the hop-count diameter of the network).
Steps when a route fails
1. R3’s s0/0.1 subinterface fails, but R1’s Frame Relay subinterface stays up—so R1 must use
its timers to detect route failures.
2. R1’s Invalid and Flush timers for route 172.31.103.0/24 grow because it does not hear any
further updates from R3.
3. After the Invalid timer expires (180 seconds) for R1’s route to 172.31.103.0/24, R1 begins a
Holddown timer for the route. Holddown starts at (default) 180 seconds, and counts down.
4. The Flush timer expires after a total 240 seconds, or 60 seconds past the Invalid timer. As a
result, R1 flushes the route to 172.31.103.0/24 from its routing table, which also removes the
Holddown timer for the route
RIP Offset Lists
RIP offset lists allow RIP to add to a route’s metric, either before sending an update, or for routes
received in an update. The offset list refers to an ACL (standard, extended, or named) to match the
routes; the router then adds the specified offset, or extra metric, to any matching routes. Any routes
not matched by the offset list are unchanged. The offset list also specifies which routing updates
to examine by referring to a direction (in or out) and, optionally, an interface. If the interface is
omitted from the command, all updates for the defined direction are examined.